DNA gyrase, which is involved in DNA replications, integrative recombination of phage lambda DNA, transcription, and DNA repair, was purified from B. subtilis. The enzyme consists of the nalidixic acid (oxolinic acid) resistance and novobiocin (coumermycin A1) resistance gene products as does E. coli enzyme. In this year, the reactions catalyzed by B. subtilis enzyme have been compared with the reactions by E. coli enzyme. Moreover, heterogous DNA gyrases have been constructed biochemically and genetically to understand universal function of the enzyme.